<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
		<style type="text/css">
			.aaa{width:200px;height:200px;
			background-color:red;}

/*opacity:透明度--------0~1
    0：不透明；
    1：全透明
    0.5：半透明*/			
    
/*IE8及以下不支持opacity，用filter:alpha(opacity=透明度)
    透明度范围0~100
    50：半透明*/    

			.bbb{width:200px;height:200px;
			background-color:yellow;
			position:relative;
			left:100px;top:-100px;
			opacity:0.5;
			filter:alpha(opacity=50)}
			
			.ccc{width:200px;height:200px;
			background-color:green;
			position:absolute;
			left:200px;top:200px;
			opacity:0.5;
			filter:alpha(opacity=50)}
		</style>
	</head>
	<body>
		<div class="aaa"></div>
		<div class="bbb"></div>
		<div class="ccc"></div>
	</body>
</html>
